Two Wireless Networks @ Once (802.11b and 802.11n)

I have a second PC and a TiVo Series 2 attached to an 802.11b wireless network. I have a new laptop coming into the family that is 802.11n. The 2nd PC might be upgradeable to "N" but the TiVo can't right now. Attaching a "b" device to an "n" network can slow the whole network down. I don't want that. I thought about having two wireless networks attached to the internet at once. Have both a "b" and "g" network running at once. The 2nd PC and TiVo can stay on the "b" network and the new laptop on an "n" network. The question is how do I hook up the two wireless routers? Can I just connect the "internet" into the "in" of one router and then connect the "in" of the second router into a wired "out" port of the first router. This isn't about expanding a wireless network. It is about having two independent wireless networks. Any advice would be great.

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